Power and thermal management issues are considerations in all segments of computer-based systems. While in the server domain, the cost of electricity drives the need for low power systems, in mobile systems battery life and thermal limitations make these issues relevant. Optimizing a system for maximum performance at minimum power consumption is usually done using the operating system (OS) or system software to control hardware elements. Most modern OS's use the Advanced Configuration and Power Interface (ACPI) standard, e.g., Rev. 3.0b, published Oct. 10, 2006, for optimizing the system in these areas. An ACPI implementation allows a processor core to be in different power-saving states (also termed low power or idle states), generally referred to as so-called C1 to Cn states.
When a core is active, it runs at a so-called C0 state, and when the core is idle, it may be placed in a core low power state, a so-called core non-zero C-state. The core C1 state represents the low power state that has the least power savings but can be entered and exited almost immediately, while an extended deep-low power state (e.g., C3) represents a power state where the static power consumption is negligible, but the time to enter/exit this state and respond to activity (i.e., back to C0) is longer.